This invention relates generally to a joint forming apparatus and specifically to a die and punch for forming a joint between sheets of material.
It is old in the art to join multiple pieces of sheet metal by punching or otherwise manipulating them to cause these sheets to be deformed into an interlocking relationship in a localized area. However, such joints have traditionally required the shearing of the sheet material and hence are not suitable for leakproof applications unless a sealant is applied. The formation of such joints is also frequently destructive of the corrosion resistance of coated materials. In addition, the known apparatuses for forming the joints are frequently complex in design. This complexity increases the cost of the equipment, as well as the energy required for operation.
More recently, the inventor of the present invention has developed an apparatus for producing more cost effective and aesthetically pleasing leakproof and lanced joints. These are known within the industry as TOG-L-LOC.RTM. and LANCE-N-LOC.RTM. joints which can be obtained from the assignee of the present invention. These improved joints are disclosed within U.S. Pat. No. 5,150,513 which issued on Sep. 29, 1992 and U.S. Pat. No. 5,177,861 which issued on Jan. 12, 1993, both of which are incorporated by reference herewithin.
Moreover, the use of coiled springs to inwardly retain a plurality of movable die pieces against an anvil for joining sheets of material is shown in Japanese Patents 148036 entitled "Joining Device for Thin Metallic Plate" and 148039 entitled "Joining Device for Metallic Sheet." However, in both of these devices, the coiled spring is not canted. Furthermore, an outer sleeve is not shown surrounding the spring and movable die pieces. These references also do not appear to disclose a stripper for use in combination with the punch.
The TOG-L-LOC.RTM. and LANCE-N-LOC.RTM. joints are commonly formed within a C-shaped toggle press. Such a toggle press is disclosed in U.S. Pat. No. 3,730,044 entitled "Fluid Operated Apparatus" which issued to the inventor of the present invention on May 1, 1973, and is incorporated by reference herewithin. Although such a conventional toggle press is cost effective and reliable, the punch and die tends to bow outward from their desired longitudinal axis during formation of a joint therebetween. Therefore, the edges of the punch and die anvil are highly stressed and may be prematurely worn or fracture.
In accordance with the present invention, the preferred embodiment of a die and punch assembly is employed to form a joint between at least two sheets of material. The preferred embodiment die has a shield surrounding an anvil. This shield has at least one aperture extending therethrough. In another aspect of the present invention a canted coil spring expandably retains at least three die blades between the shield and the anvil. In a further aspect of the present invention, the shield is snappably engagable with a die body. In yet another aspect of the present invention, an upper edge of at least one die blade is substantially coplanar with an upper edge of the shield prior to a joint being formed thereagainst. In still another aspect of the present invention, either the anvil, punch, or both has a frusto conical taper disposed along a peripheral edge thereof. In another aspect of the present invention, an external surface of a stripper has substantially the same diameter as does an outside surface of the shield.
The die and punch assembly of the present invention are advantageous over conventional devices in that an aperture in the present invention die shield allows for self-cleaning during operation. The present invention die shield and blades are also advantageous by having substantially coplanar upper edges so as to provide additional sheet material support during joint formation. Another advantage of the present invention is that the frusto conical taper on the punch, anvil, or both peripheral edge prevents high stress concentrations and improves the tool life. The snap together construction of the shield and die body allows for easy and low cost assembly and processing while achieving more uniform tolerances during heat treating. Additional advantage and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.